Radio apparatus with diversity antennas

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a radio apparatus having multiple separate antennas, and in particular to a radio apparatus suitable for a portable transceiver or a portable receiver.

2. Description of the Related Art

In a radio apparatus having a pair of separate antennas providing spatial diversity, especially in a portable radio apparatus, it is difficult to ensure a sufficient spacing between the separate antennas, respectively. This causes isolation between antenna devices to be reduced, resulting in deterioration of antenna gain.

To overcome such a problem, a radio apparatus capable of selectively terminating the diversity antennas has been proposed in Japanese Patent Unexamined publication No. 7-202774. This conventional radio apparatus is provided with an antenna terminating system including a monopole antenna and a small size antenna which are connected to first and second antenna terminators through first and second switch devices, respectively. When the received signal level of the monopole antenna is higher than that of the small size antenna, the monopole antenna is connected to a receiver by the first switch device and the small size antenna is connected to the second antenna terminator by the second switch device. Otherwise, the monopole antenna is connected to the first antenna terminator by the first switch device and the small size antenna is connected to the receiver by the second switch device.

SUMMARY OF THE INVENTION

In the conventional radio apparatus mentioned above, a radio-frequency (RF) amplifier is not provided at the stage preceding the receiver. Therefore, a radio signal received by the receiver is reduced in signal level by feeder lines and the switch device, resulting in deterioration of the accuracy of received level detection. Further, the first and second switch devices must use a single-pole double-throw switch for selecting one of the paths to the receiver and the antenna terminator, resulting in difficulty in meeting the needs of both effective isolation and miniaturization.

An object of the present invention is to provide a radio apparatus which is capable of receiving radio signals through multiple antennas while meeting the needs of both miniaturization and improved isolation between multiple antennas.

Another object of the present invention is to provide a radio apparatus which is capable of ensuring the improved isolation and a sufficient level of received radio signal received through multiple antennas.

According to the present invention, each of a plurality of receiving systems is provided with an antenna terminator and a path control switch. The antenna terminator selectively terminates a corresponding antenna of the multiple antennas and the path control switch selectively switches on and off to provide a path for a radio signal received by the corresponding antenna. The antenna terminator and the path control switch are controlled such that an antenna terminator is inactive and a path control switch is on in a selected receiving system and, contrarily, an antenna terminator is active and a path control switch is off in the other receiving system.

Since an antenna terminator is inactive and a path control switch is on in a selected receiving system and an antenna terminator is active and a path control switch is off in the other receiving system, the isolation between multiple antennas is improved, promoting miniaturization.

The path control switch may be a preamplifier which is selectively on and off. When the preamplifier is on, the path is provided. When the preamplifier is off, the path is blocked off. More specifically, each receiving system includes an antenna terminator and a preamplifier. The preamplifier amplifies a radio signal received by the corresponding antenna, the preamplifier being selectively active and inactive. Further, the radio apparatus is comprised of a discriminator for discriminating one receiving system from another receiving system based on radio signals received by the receiving systems, respectively, and a controller for controlling the one receiving system such that an antenna terminator is inactive and a preamplifier is active to produce an amplified radio signal to be used as a received signal and controlling the other receiving system such that an antenna terminator is active and a preamplifier is inactive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an radio apparatus according to an embodiment of the present invention;

FIG. 2A is a diagram showing a matching line of a first receiving circuit as shown in FIG. 1;

FIG. 2B is a diagram showing a matching line of a second receiving circuit as shown in FIG. 1;

FIG. 3 is a time chart showing ON/OFF operations of radio-frequency switches and preamplifiers according to the embodiment; and

FIG. 4 is a block diagram showing an radio apparatus according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a radio apparatus according to a first embodiment of the present invention is comprised of a first receiving system and a second receiving system. The first receiving system includes a first antenna 101 connected to a first antenna matching line 102 through which the first antenna 101 is connected to a band-pass filter 103. A radio-frequency switch RF-SW₁ connects a predetermined position of the first antenna matching line 102 to ground depending on a switch control signal S_SW1. The RP switch RF-SW₁ is a single-pole-single-throw switch which may be a semiconductor switch such as a diode switch or a small-size relay switch. The band-pass filter 103 is further connected to an RF preamplifier 104 which is selectively active and inactive, in other words, powered on and off, according to a power control signal S_AMP1. When powered on, the RF preamplifier 104 amplifies a first received radio signal passing through the band-pass filter 103 to produce a first amplified radio signal S_R1.

The second receiving system includes a second antenna 105 connected to a second antenna matching line 106 through which the second antenna 105 is connected to a duplexer 107. A radio-frequency switch RF-SW₂ connects a predetermined position of the second antenna matching line 106 to ground depending on a switch control signal S_SW2. The RF switch RF-SW₂ is a single-pole single-throw switch which may be a semiconductor switch such as a diode switch or a small-size relay switch. The duplexer 107 is connected to a band-pass filter 108 for reception. The band-pass filter 108 is further connected to an RF preamplifier 109 which is selectively active and inactive, in other words, powered on and off, according to a power control signal S_AMP2. When powered on, the RF preamplifier 109 amplifies a second received radio signal passing through the band-pass filter 108 to produce a second amplified radio signal S_R2.

The respective output signals S_R1 and S_R2 of the RF preamplifiers 104 and 109 are input to a radio receiver 110. As will be described later, the output signals S_R1 and S_R2 are alternately input to the radio receiver 110 during level detection periods and, during receiving periods, only a selected output signal S_R1 or S_R2 is input to the radio receiver 110. The radio receiver 110 includes a frequency converter, a demodulator, a signal level detector and other necessary circuits (not shown) and outputs a detected signal level R_SI and a demodulated baseband signal to a controller 111 such as TDMA synchronization controller. The controller 111 controls the RF switches RF-SW₁ and RF-SW₂ using the switch control signals S_SW1 and S_SW2, respectively, and the RP preamplifiers 104 and 109 using the power on/off control signals S_AMP1 and S_AMP2, respectively.

A radio transmitter 112 includes a modulator, a frequency converter and other necessary circuits (not shown) and is connected to the duplexer 107 through a band-pass filter 113. Therefore, the second antenna 105 can be used for both reception and transmission through the duplexer 107. The component circuits of the radio apparatus are controlled by a processor 114. Further, a battery 115 including a power controller may be used as a power supply of the apparatus.

Referring to FIG. 2A, the first antenna matching line 102 is connected to the first antenna 101 at a feeding point 201 and is further connected to the band-pass filter 103 at its input terminal 202. Further, the predetermined position 203 of the first antenna matching line 102 is connected to one terminal of the RF switch RF-SW₁ which is grounded at the other terminal. In this embodiment, a first line length from the feeding point 201 to the predetermined position 203 and a second line length from the predetermined position 203 to the input terminal 202 of the band-pass filter 103 are set to L1 and L2, respectively.

When the RF switch RF-SW₁ is off or open, the feeding point 201 is connected to the input terminal 202 of the band-pass filter 103 through a total length L1+L2 of the first antenna matching line 102. The total line length L1+L2, the impedance and the configuration of the first antenna matching line 102 are designed to maximize the antenna gain of the first antenna 101 when the RF switch RF-SW₁ is off.

On the other hand, when the RF switch RF-SW₁ is on or closed, the predetermined position 203 of the first antenna matching line 102 is connected to ground through the RF switch RF-SW₁. The first length L1 and the second length L2 are designed to minimize the antenna gain of the first antenna 101 when the RF switch RF-SW₁ is on. Needless to say, the length and configuration of the first antenna matching line 102 vary according to the type, length and other parameters of the first antenna 101.

Similarly, the second antenna matching line 106 is formed as described above. Referring to FIG. 2B, the second antenna matching line 106 is connected to the second antenna 105 at a feeding point 204 and is further connected to the duplexer 107 at its input terminal 205. Further, the predetermined position 206 of the second antenna matching line 106 is connected to one terminal of the RF switch RF-SW₂ which is grounded at the other terminal. In this embodiment, a third line length from the feeding point 204 to the predetermined position 206 and a fourth line length from the predetermined position 206 to the input terminal 205 of the duplexer 107 are set to L3 and L4, respectively.

When the RF switch RF-SW₂ is off or open, the feeding point 204 is connected to the input terminal 205 of the duplexer 107 through a total length L3+L4 of the second antenna matching line 106. The total line length L3+L4, the impedance and the configuration of the second antenna matching line 106 are designed to maximize the antenna gain of the second antenna 105 when the RF switch RF-SW₂ is off.

On the other hand, when the RF switch RF-SW₂ is on or closed, the predetermined position 206 of the second antenna matching line 106 is connected to ground through the RF switch RF-SW₂. The third length L3 and the fourth length L4 are designed to minimize the antenna gain of the second antenna 105 when the RF switch RF-SW₂ is on. Needless to say, the length and configuration of the second antenna matching line 106 vary according to the type, length and other parameters of the second antenna 105.

A level detection of a received radio signal, switching operations of the RF switches RF-SW₁ and RF-SW₂ and power control of the RF preamplifiers 104 and 109 will be described in detail hereinafter, assuming that the radio apparatus is a mobile terminal which can be used in a mobile communication system of Time-Division Multiple Access scheme (TDMA). In the TDMA system, a base station transmits a radio signal such as a control signal or a communication signal to a lot of mobile terminals located in its service area through a control channel or a communication channel including a plurality of predetermined assigned time slots.

Referring to FIG. 3, during a time period ΔT of a slot M between a transmission (TX) channel and a reception (RX) channel, the processor 114 instructs the controller 111 to sequentially output the switch control signals S_SW2 and S_SW1 to the RF switches RF-SW₂ and RF-SW₁, respectively, and to sequentially output the power on/off control signals S_AMP1 and S_AMP2 to the RF preamplifiers 104 and 109, respectively. In other words, the RF switches RF-SW₁ and RF-SW₂ alternatively become on (active) and off (inactive) so that one is on when the other is off The RF preamplifiers 104 and 109 alternately become on (active) and off (inactive) so that one is on when the other is off. More specifically, when both the RF switches RF-SW₂ and the RF preamplifier 104 are on, a received radio signal from the first antenna 101 is amplified by the RF amplifier 104 and the amplified radio signal S_R1 is output to the radio receiver 110. The radio receiver 110 outputs a detected signal level R_SI1 of the received radio signal S_R1 to the controller 111.

On the other hand, when both the RF switches RF-SW₁ and the RF preamplifier 109 are on, a received radio signal from the second antenna 105 is amplified by the RF preamplifier 109 and the amplified radio signal S_R2 is output to the radio receiver 110. The radio receiver 110 outputs a detected signal level R_S12 of the received radio signal S_R2 to the controller 111. When receiving the detected signal levels R_SI1 and R_SI2, the controller 111 compares them and, based on the detected signal levels during the level detection period, selects an antenna of better receiving condition, that is, a receiving system of a higher detected signal level.

It is assumed that R_SI1 is greater than R_SI2 during the level detection period, that is, a received signal of the first antenna 101 provides a better receiving condition than that of the second antenna 105. In this case, when a reception channel has come, the controller 111 outputs the respective switch control signals S_SW1 and S_SW2 to the RF switches RF-SW₁ and RF-SW₂ so that the RF switch RF-SW₁ is turned off and the RF switch RF-SW₂ is turned on. At the same time, the controller 111 outputs the respective power on/off control signals S_AMP1 and S_AMP2 to the RF preamplifiers 104 and 109 so that the RP preamplifier 104 becomes on and the RF preamplifier 109 becomes off. Therefore, during the reception channel, with maximizing the antenna gain of the first antenna 101 and minimizing that of second antenna 105, the only the received radio signal S_R1 of the RF preamplifier 104 is selected and received by the radio receiver 110. Since the antenna gain of the second antenna 105 is minimized and the RF preamplifier 109 is inactive, the coupling of the second antenna system with the first antenna system is dramatically reduced.

In cases where R_SI1 is smaller than R_SI2 during a level detection period, that is, a received signal of the second antenna 105 provides a better receiving condition than that of the first antenna 101, in a reception channel, the controller 111 outputs the respective switch control signals S_SW1 and S_SW2 to the RF switches RF-SW₁ and RF-SW₂ so that the RF switch RF-SW₁ is turned on and the RF switch RF-SW₂ is turned off. At the same time, the controller 111 outputs the respective power on/off control signals S_AMP1 and S_AMP2 to the RF preamplifiers 104 and 109 so that the RF preamplifier 104 becomes off and the RF preamplifier 109 becomes on. Therefore, during the reception channel, with maximizing the antenna gain of the second antenna 105 and minimizing that of the first antenna 101, only the received radio signal S_R2 of the RF preamplifier 109 is selected and received by the radio receiver 110. Since the antenna gain of the first antenna 101 is minimized and the RF preamplifier 101 is inactive, the coupling of the first antenna system with the second antenna system is dramatically reduced.

FIG. 4 shows a radio apparatus according to a second embodiment of the present invention, where circuit blocks similar to those previously described with reference to FIG. 1 are denoted by the same reference numerals. Further, since operations of these circuit blocks are similar to those previously described with reference to FIG. 1, their descriptions are omitted.

Referring to FIG. 4, the radio apparatus is comprised of a first receiving system and a second receiving system. The first receiving system includes a first antenna 101 connected to a first antenna matching line 301 through which the first antenna 101 is connected to the band-pass filter 103. The first antenna matching line 301 includes an RF switch RF-SW₃ at a predetermined position thereof. The predetermined position is determined in the same way as described in FIG. 2.

The RF switch RF-SW₃ is a single-pole double-throw switch which may be a semiconductor switch such as a diode switch or a small-size relay switch. The common terminal of the RF switch RF-SW₃ is connected to the first antenna 101 through a part of the first antenna matching line 301, the first terminal of the RF switch RF-SW₃ is connected to the band-pass filter 103 through the other part of the first antenna matching line 301, and the second terminal of the RP switch RF-SW₃ is connected to ground through an antenna terminator 302. The RF switch RF-SW₃ connects the first antenna 101 to a selected one of the band-pass filter 103 and the antenna terminator 302 depending on the switch control signal S_SW1.

When the RF switch RF-SW₃ is in first-terminal position, The total line length, the impedance and the configuration of the first antenna matching line 301 are designed to maximize the antenna gain of the first antenna 101. On the other hand, when the RF switch RF-SW₃ is in second-terminal position, the second terminal of the RF switch RF-SW₃ is connected to ground through the antenna terminator 302. Therefore, the impedance of the antenna terminator 302 are designed to minimize the antenna gain of the first antenna 101 when the RF switch RF-SW₁ is in second-terminal position. Needless to say, the length and configuration of the first antenna matching line 301 and the impedance of the antenna terminator 302 vary according to the type, length and other parameters of the first antenna 101.

It is the same with the second antenna matching line 303 including an RF switch RF-SW₄ and a second antenna terminator 304. Therefore, its detailed description is omitted.

In such a configuration, the signal level detection is also performed as described in FIG. 3. When the received signal level of the first antenna 101 is higher than that of the second antenna 105, the first antenna 101 is connected to the band-pass filter 103 by the RF switch RF-SW₃ switching to the first terminal. At the same time, the second antenna 105 is connected to the second antenna terminator 304 by the RF switch RF-SW₄ switching to the second terminal and the RF preamplifier 109 is powered off. Since the antenna gain of the second antenna 105 is minimized and the RF preamplifier 109 is inactive, the coupling of the second antenna system with the first antenna system is dramatically reduced.

When the received signal level of the first antenna 101 is smaller than that of the second antenna 105, the first antenna 101 is connected to the first antenna terminator 302 by the RF switch RF-SW₃ switching to the second terminal and, at the same time, the second antenna is connected to the duplexer 107 by the RF switch RF-SW₄ switching to the first terminal. Since the antenna gain of the first antenna 101 is minimized and the RF preamplifier 101 is inactive, the coupling of the first antenna system with the second antenna system is dramatically reduced.

It is apparent that the present invention can be applied to another radio apparatus including three or more receiving systems In this case, the RF preamplifiers of the receiving systems may be powered on one-by-one in a predetermined period to produce the received radio signals which are used to detect signal levels.